Forensic science, also known as criminalistics, is the application of science to criminal and civil laws. During criminal investigation in particular, it is governed by the legal standards of admissible evidence and criminal procedure. It is a broad field utilizing numerous practices such as the analysis of DNA, fingerprints, bloodstain patterns, firearms, ballistics, and toxicology.
A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfaces such as glass or metal. Deliberate impressions of entire fingerprints can be obtained by ink or other substances transferred from the peaks of friction ridges on the skin to a smooth surface such as paper. Fingerprint records normally contain impressions from the pad on the last joint of fingers and thumbs, though fingerprint cards also typically record portions of lower joint areas of the fingers.
Staining is a technique used to enhance contrast in samples, generally at the microscopic level. Stains and dyes are frequently used in histology, in cytology, and in the medical fields of histopathology, hematology, and cytopathology that focus on the study and diagnoses of diseases at the microscopic level. Stains may be used to define biological tissues, cell populations, or organelles within individual cells.
Steatosis, also called fatty change, is abnormal retention of fat (lipids) within a cell or organ. Steatosis most often affects the liver – the primary organ of lipid metabolism – where the condition is commonly referred to as fatty liver disease. Steatosis can also occur in other organs, including the kidneys, heart, and muscle. When the term is not further specified, it is assumed to refer to the liver.
Dye penetrant inspection (DP), also called liquid penetrate inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to check surface-breaking defects in all non-porous materials. The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.
Histopathology refers to the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopathology refers to the examination of a biopsy or surgical specimen by a pathologist, after the specimen has been processed and histological sections have been placed onto glass slides. In contrast, cytopathology examines free cells or tissue micro-fragments.
The Ziehl-Neelsen stain, also known as the acid-fast stain, is a bacteriological staining technique used in cytopathology and microbiology to identify acid-fast bacteria under microscopy, particularly members of the Mycobacterium genus. This staining method was initially introduced by Paul Ehrlich (1854–1915) and subsequently modified by the German bacteriologists Franz Ziehl (1859–1926) and Friedrich Neelsen (1854–1898) during the late 19th century.
Sudan IV (C24H20N4O) is a lysochrome (fat-soluble dye) diazo dye used for the staining of lipids, triglycerides and lipoproteins on frozen paraffin sections. It has the appearance of reddish brown crystals with melting point 199 °C and maximum absorption at 520(357) nm.
Sudan III is a lysochrome diazo dye. It is structurally related to azobenzene.
Solvent Black 3 is an azo dye. It is a non-fluorescent, relatively thermostable lysochrome diazo dye used for staining of neutral triglycerides and lipids on frozen sections and some lipoproteins on paraffin sections. It has the appearance of a dark brown to black powder with maximum absorption at 596–605 nm and melting point 120–124 °C. It stains blue-black.
Sudan II (Solvent Orange 7, C.I. 12140, C18H16N2O) is a lysochrome (fat-soluble dye) azo dye used for staining of triglycerides in frozen sections, and some protein bound lipids and lipoproteins on paraffin sections. It has the appearance of red powder with melting point 156–158 °C and maximum absorption at 493(420) nm.
Hematoxylin and eosin stain is one of the principal tissue stains used in histology. It is the most widely used stain in medical diagnosis and is often the gold standard. For example, when a pathologist looks at a biopsy of a suspected cancer, the histological section is likely to be stained with H&E.
Sudan stains and Sudan dyes are synthetic organic compounds that are used as dyes for various plastics and are also used to stain sudanophilic biological samples, usually lipids. Sudan II, Sudan III, Sudan IV, Oil Red O, and Sudan Black B are important members of this class of compounds.
Fingerprint powders are fine powders used, in conjunction with fingerprint brushes, by crime scene investigators and other law enforcement personnel to search for and enhance latent/invisible fingerprints that can be used to determine identification. This method of fingerprint development commonly referred to as dusting for fingerprints, involves the adherence of the powder particles to the moisture and sweat secretions deposited on to surfaces by the raised ridges on fingers, palms, or soles of feet designed for grip, called friction ridges.
Lawsone (2-hydroxy-1,4-naphthoquinone), also known as hennotannic acid, is a red-orange dye present in the leaves of the henna plant, for which it is named, as well as in the common walnut and water hyacinth. Humans have used henna extracts containing lawsone as hair and skin dyes for more than 5,000 years. Lawsone reacts chemically with the protein keratin in skin and hair via a Michael addition reaction, resulting in a strong permanent stain that lasts until the skin or hair is shed. Darker colored staining is due to more lawsone–keratin interactions occurring, which evidently break down as the concentration of lawsone decreases and the tattoo fades. Lawsone strongly absorbs UV light, and aqueous extracts can be effective sunless tanning agents and sunscreens. Lawsone is a 1,4-naphthoquinone derivative, an analog of hydroxyquinone containing one additional ring.
Toluidine blue, also known as TBO or tolonium chloride (INN) is a blue cationic (basic) dye used in histology and sometimes clinically.
Alexandre Beaudoin is a Quebec fingerprint scientist known for inventing a technique for developing latent fingerprints on dry and/or wet porous surfaces.
Brian E. Dalrymple is an Ontarian fingerprint scientist known for introducing for the first time the use of lasers as a forensic light sources for fingerprints and other evidence detection, using the Argon Ion Lasers to detect the inherent fluorescence of the latent fingerprints and finding fluorescing evidence. That was the beginning of a real revolution in the forensic identification field. Brian Dalrymple also become the first to use this forensic technique on a real case.
Luxol fast blue stain, abbreviated LFB stain or simply LFB, is a commonly used stain to observe myelin under light microscopy, created by Heinrich Klüver and Elizabeth Barrera in 1953. LFB is commonly used to detect demyelination in the central nervous system (CNS), but cannot discern myelination in the peripheral nervous system.
Glove prints, also sometimes described as gloveprints or glove marks, are latent, fingerprint-like impressions that are transferred to a surface or object by an individual who is wearing gloves.
